A number of different handling processes are used to process continuous webs of material into defined segments, such as discrete webs cut from a continuous web for subsequent processing. In general, a manufacturing line in which the discrete webs are used includes a pre-wound roll of the continuous web of material that is unwound by a suitable drive mechanism and fed (often through various stations of the manufacturing line) to a cutting station at which the web is cut sequentially into discrete webs of the material. Typically, the continuous web is held in tension as it is transported from the wound roll to the cutting station. The discrete webs are then transported away from the cutting station to another station of the manufacturing line at which the discrete webs are assembled with other components of the product being formed.
Typically, the drive mechanism attempts to maintain a constant tension in the web of material as unexpected changes in tension at one or more points in the manufacturing line may result in undesired tears or breaks in the continuous web of material. Such tears or breaks disrupt the manufacturing process and may cause significant downtime and/or costs to be incurred.
One or more speed setpoints are used to control the unwinding speed of the continuous web of material. If variations occur between the speed setpoint and the actual speed of the web at different points along the web of material, the tension may become mismatched along the web of material. The drive mechanism attempts to track the actual speed of the web to the speed setpoint as closely as possible by controlling the torque generated by the motor.
As the roll of the material is unwound, the inertia of the roll changes. More specifically, the inertia of the roll is based on the density of the material and the amount of material remaining on the roll. At least some known systems use inertia compensation algorithms to adjust the torque of the drive mechanism to compensate for the change in inertia due to the unwinding of the roll. The algorithms typically include a “hardcoded,” or static, value for the density of the material, for example, based on a typical or baseline density of the material as measured at a prior point in time. However, the density of the material may change based on environmental factors such as humidity, temperature, and the like, and/or based on other factors. Accordingly, algorithms used in industry today do not accurately compensate for the inertia of the roll of material as it is unwound due to variations in density, thus causing a risk that the continuous web of material may break or tear.